Wireless communication systems are widely used to provide voice and data services for multiple users using a variety of access terminals such as cellular telephones, laptop computers and various multimedia devices. Such communications systems can encompass local area networks, such as IEEE 801.11 networks, cellular telephone and/or mobile broadband networks. The communication system can use a one or more multiple access techniques, such as Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), Code Division Multiple Access (CDMA), Orthogonal Frequency Division Multiple Access (OFDMA), Single Carrier Frequency Division Multiple Access (SC-FDMA) and others. Mobile broadband networks can conform to a number of system types or partnerships such as, General Packet Radio Service (GPRS), 3rd-Generation standards (3G), Worldwide Interoperability for Microwave Access (WiMAX), Universal Mobile Telecommunications System (UMTS), the 3rd Generation Partnership Project (3GPP), Evolution-Data Optimized EV-DO, or Long Term Evolution (LTE).
An illustration of a conventional mobile broadband system 100 is illustrated in FIG. 1. Mobile broadband system is divided into cells 108, 110 and 112, where each cell 108, 110 and 112 has corresponding base station 102, 104 and 106. Mobile terminals or user equipment (UE) 116 and 114 access network 100 through one of base stations 102, 104 and 106. Three base stations 108, 110 and 112 and two UEs 114 and 116 are used for simplicity of illustration, however, multiple cells and UEs can be used and provided for in real systems.
In communication systems such as CDMA and LTE, bandwidth is shared among terminal devices or UEs in the uplink communications channel. Because bandwidth is shared, power control is used in the uplink communications to address the near-far effect. This means that UE 114 at the cell edge with higher path loss PL2 to base station 102 will generally transmit with a higher power than UE 116 with lower path loss PL1 so that each respective transmission is received at a reasonable level above noise and interference.
The prior art has addressed the power control in a couple of ways. Under the full power control (FPC) scheme, the received signal level of all UEs are about the same at the base station in order to provide equal signal to noise and interference ratio (SNIR) for all users. Under FPC, the UE power is set to fully compensate for the channel loss, thus all users have same received signal level Po at the base station:P0={10*log 10(N+I0)+SNIRTARG},  (1)where, I0 is the estimated total interference power at the base station, N is the thermal noise power, and SNIRTARG is the target SNIR. The transmit power at the UE under FPC is given by:Pƒ={Pmax,P0+PL},  (2)
Where Pmax is a maximum transmit power a UE is allowed to transmit and PL is the path loss. It can be seen that using FPC, all UEs have the same SNIR if the target SNIR is the same for all UEs and if UE power is not limited by Pmax. When FPC is used, however, the same modulation and coding scheme (MCS) level is typically used by all the UEs, which potentially results in a reduced system throughput because higher MCS levels are not used.
The fractional power control (FrPC) scheme proposed in the LTE standard allows users with lower path loss to use a higher power level than would be otherwise required to maintain a minimum SNIR threshold. The allowed margin above the cell edge SNIR is inversely proportional to the path loss of the user, so that a user in closer proximity to the base station can obtain a higher SNIR and a higher MCS level. The transmitter power of a UE under FrPC is expressed as:Ptx{Pmax,P′0+α.PL} and P′0=P0+Δ0,where α is a multiplier that is less than 1, and Δ0 is a power increase factor set such that the cell-edge UEs still achieves the target SNIR. (When α is equal to 1, the system operates as a FPC system.) Under FrPC, UEs that are closer to the base station can boost power above the point that would have been set by FPC, where the increase in power ΔP is given by:ΔP=(1−α)×(PL−PLcell—edge),so that Ptx=ΔP+Pƒwhere PLcell—edge is the path loss from the cell edge UE to the base station.
UEs closer to the base station, therefore, have a higher SNIR than UEs farther from the base station. While FrPC shows some improvement over FPC schemes, FrPC chooses UE transmission levels based on a UE path loss and not based on the actual interference level being caused by the UE. Consequently, FrPC power control may not effectively reduce interference in some cases.
What is needed are systems and method of power control for multiple access wireless networks that increase throughput and minimize interference.